When in Sweden, of course you should get some literature to bring home with you...!
As you perhaps know already Astrid Lindgren was Swedish, and her childrens books are classics. Other famous Swedish authors include August Strindberg and Selma Lagerlöf (Ibsen, however, was Norwegian).
Good bookstores are located right in the city center. Within the Central Staion buiding for example there are already two paperback stores, one on ground level and the other below ground. They are called Pocketshop (a pocket in Swedish means a paperback book, probably indicating that it is small enogh to carry in your pocket - why the english word is used, though, is a mystery). These offer a selection of paperback books by both native and foreign authors.
Facing the Sergel Square, on the opposite side of it from Kulturhuset is one big store from the bookstore-chain Akademibokhandeln. English and Swedish books, both hardback anbd paperback are for sale, as are severqal guide books and maps.
An even wider range is offered by another Akademibokhandeln store on Norrlandsgatan, just opposite the NK department store. If you are looking for English books, this is the place to go.
What to buy: Popular present-day authors in Sweden are for example
Try one of Jonas Gardells books, if you don't know what to choose, he has written several books with a setting in 1970's Sweden, with an acknowledged eye for the feeling of the time.
What to pay: Swedish paperback books usually cost between € 5 and € 7. English paperback from about € 9. Hardbacks are much more expensive. Look for special offers and "Buy 4 pay for 3" and similar campaigns.
The Sweden Bookshop is a large bookstore on Gamla Stan. It stocks titles in English, Swedish and other languages, including guidebooks.
What to buy: Books!
What to pay: Variable.